Once you have completed and saved your scenario, you can now share it with other users. The mod files are located in your AppData\LocalLow folder. Your scenario should be in a folder matching the name you gave it during creation.
To share on Nexus Mods, you need to first create an archive containing your mods files. We recommend using 7zip. Simply right-click on your mod folder and select "Send to -> Compressed (zipped) folder" (or if you are using 7zip, "7-zip -> Add to archive...".
Then you can upload your mod to Nexus Mods here.
To share your mod on the Steam Workshop, you can use the "Save and publish" option in the Scenario Editor.